Orthogonal multiple access (OMA) techniques have been traditionally utilized to enhance system throughput and satisfy the required quality of service (QoS) requirements. OMA systems serve multiple users using orthogonal time, frequency, or code resources to prevent intra-cell interference between users. However, such orthogonality limits the number of users served simultaneously by the same base station (BS). Non-orthogonal multiple access (NOMA) techniques have been proposed to enhance spectral efficiency, distinguishing users in the power domain. In NOMA, multiple users are allowed to share the same time-frequency-code resources, and interference is mitigated using signal processing techniques [1]}, [2]}. Although spectrum scarcity is not the primary concern at the THz band, there are several motivations for THz-NOMA. Due to hardware limitations, the THz band has not been fully conquered yet, and hence efficient utilization of the available bandwidths remains crucial. Higher spectral efficiency sustains higher data rates using fewer costly THz resources. Moreover, diversity in the power domain could help NOMA users to overcome the highly correlated THz channels of users. Furthermore, THz-NOMA can enhance user fairness by bridging the severe power difference between the received signals of users at different distances from the BS through proper power allocation schemes [2]}.
